Screen electrode for color cathode ray tube



Feb. 22, 1966 R. D. THOMPSON SCREEN ELECTRODE FOR COLOR CATHODE RAY TUBE Filed Oct. 14, 1965 United States Patent 3,237,038 SCREEN ELECTRODE FOR COLOR CATHODE RAY TUBE Roger D. Thompson, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed Oct. 14, 1963, Ser. No. 315,818 11 Claims. (Cl. 31389) This invention relates to cathode ray tubes for producing color images. The invention is particularly directed to a screen electrode for such tubes wherein the screen electrode includes means for generating indexing signals for the purpose of synchronizing the scan and color modulation of the electron beam with each other. Such tubes are known as feedback or sensing tubes.

One prior art embodiment of sensing color cathode ray tubes may include a screen electrode having a mosaic of different primary color emitting phosphor strips, e.g., redemitting, green-emitting, and blue-emitting. The strips are straight-sided, contiguous with each other, and are arrayed parallel to each other and perpendicular to the direction of beam scan. Suitable indexing signals are generated from a plurality of spaced-apart strips of electron sensitive material, such as ultraviolet light emitting phosphor, which are systematically disposed relative to the color phosphor strips of the mosaic on the back thereof.

In operation of a tube of the type described above, if it is desired to illuminate a portion of the screen in a primary color (red, blue, or green), the electron beam is intermittently turned on as it scans over those phosphor strips which will emit the desired primary color. If it is desired to illuminate a portion of the screen in a secondary color, the electron beam is turned on as it scans over a plurality of different primary-color-emitting phosphor strips which mix together to produce the secondary color. For example, if a secondary color of yellow hue is desired, the electron beam is turned on as it scans over the red and green primary phosphor strips.

In some sensing systems, the beam may be slowed down or stopped on a particular phosphor or phosphors whose luminescence is desired. Such practice is referred to as spot arrest. In producing a secondary color with spot arrest operation, the beam can be stopped or slowed down on the boundary between two primary color phosphor areas so that it excites both of the primary color phosphors more or less simultaneously in desired proportions to produce the desired secondary color.

In prior art tubes, the operation of turning on the beam during its scan across, or arrest on, the boundary of two primary color phosphor strips so as to produce a secondary color is quite critical. For example, in a spot arrest system, if the desired secondary color calls for equal parts of two different primary colors, the beam must be turned on when its spot is exactly half on each of the two primary color phosphors. If the position of the beam varies only a small distance from this desired position, the produced luminescence will be of the wrong color.

It is an object of this invention to provide an improved screen electrode for a sensing type color cathode ray tube.

It is also an object of this invention to provide an improved sensing type color cathode ray tube wherein secondary colors may more easily and accurately be produced than in prior art tubes of the same general type.

According to the invention, a mosaic of diiferent color emitting phosphors in a screen electrode of a sensing type color cathode ray tube comprises primary color emitting elemental areas spaced apart from each other. Between any two adjacent primary color elemental areas is a secondary color emitting elemental area having discrete sub- "ice elemental areas of each of the phosphors of the two adjacent primary color emitting areas. The sub-elemental areas are orderly arranged and are of a discrete size larger than that of an individual phosphor particle. The sub-elemental areas may, for example, be provided as the serrations of abutting primary color areas which have serrated edges meshed with each other.

In the drawings,

FIGURE 1 is a longitudinal sectional View of a cathode ray tube embodying the invention,

FIGURE 2 is an enlarged fragment in perspective of the tube of FIGURE 1 with parts broken away illustrat ing oneembodiment of the invention,

FIGURE 3 is a plan view of a portion of the FIGURE 2 fragment,

FIGURES 4 and 5 are plan views similar to that of FIGURE 3 illustrating alternative embodiments of the invention, and

FIGURE 6 is an enlarged view of a portion of FIG- URE 5.

Referring to FIGURE 1, a cathode ray tube 10 comprises an envelope 12 having a tubular neck 14, a faceplate 16, and an interconnecting funnel 18. An electron gun 20 is disposed in the neck 14 and is adapted to project an electron beam onto a screen electrode 22 disposed on the internal surface of the faceplate 16. The screen electrode 22 comprises a mosaic phosphor layer 24 in contact with the faceplate 16, a metallic light-reflective layer '26 on the mosaic 24, and indexing means 28 on the metallic layer 26.

As shown more clearly in FIGURE 2, the mosaic 24 of the screen electrode 22 comprises an array of red-emitting phosphor strips R, an array of blue-emitting phosphor strips B, and an array of green-emitting phosphor strips G. Thesethree arrays of phosphor strips are interleaved with each other so that the phosphor strips constitute a plurality of recurring groups, each of which groups includes one R, one B, and one G strip. The phosphor strips R, B, and G are disposed generally parallel to each other and substantially perpendicular to the direction of beam scan thereacross. Each of the phosphor strips R, B, G has serrated edges 29 which mesh with those of its adjacent strips.

The light refiectivc metallic layer 26 is disposed in overlying relationship with the mosaic 24. It may be provided according to known practices as an evaporated layer of aluminum.

The indexing means 28 comprises spaced-apart strips of ultraviolet-emitting phosphor designated as UV in the drawing. The indexing strips 28 are systematically disposed in some desired relationship with the phosphor strips R, B, and G, of the mosaic 24. For example, one UV-emitting indexing strip 28 may be provided for every three groups of three color phosphor strips R, B, G and may have a width approximately one-half of that of the combined width of the three color groups.

The UV indexing strips 28 are shown by way of example only. In accordance with known practices, other kinds and designs of indexing means may be provided. For example, an array of spaced apart strips of material having a different secondary electron emission characteristic from that of the metallic layer 26 on which they are disposed may be provided. Also, the width and periodicity of the indexing strips 28 relative to the phosphor strips R, B, G may be made diiferent from that shown. For example, one indexing strip for each group of three phosphor strips R, B, B may be provided.

In the cathode ray tube 10, wherein UV-emitting indexing means is employed, a window 30 (FIGURE 1) is provided in the funnel 18. A suitable UV-sensitive device, e.g., a phototube (not shown), may be disposed outside the envelope 12 adjacent to the window 30 to detect the UV emission generated as the electron beam scans across the screen electrode 22.

FIGURE 3, which is an enlarged plan view of the mosaic 24 of FIGURE 2, best shows the novel nature of the mosaic 24. Unlike prior art line screen mosaics having straight-sided, contiguous primary color phosphor strips, the phosphor strips R, B, G of the mosaic 24 are provided with the serrated edges 29 which mesh with those of the adjoining strips. The mosaic 24 may be thought of as comprising primary color strips of width P which are spaced from their adjacent primary strips by a distance S. The spacings S between adjacent primary color strips may be thought of as secondary color strips 32 made up of an orderly array of triangular subelemental areas (the serrations 34 of the R, B, G strips) of phosphor like that of each of the two adjacent primary color strips. Each sub-elemental area is of a discrete size larger than individual phosphor particle size.

In the mosaic 24, the pitch h of the serrations 34 is preferably a fraction of the diameter of the beam spot which scans the screen electrode 22. Thus, when a secondary color emission is desired and the scanning beam spot is turned on as it scans across, or is arrested on, the secondary strip 32, the beam spot bombards an area which includes a plurality of sub-areas of different phosphors, each of which is smaller than the beam spot itself. The bombarded area thus functions much like a separate strip made up of a phosphor which emits a secondary color. Because the boundary between any two adjacent primary strips has a finite width S, which has color response characteristics of both of the primaries,

the timing relationship between beam spot position and beam modulation is less critical than is the case with prior art straight-sided contiguous primary color strips. Accordingly secondary colors can more easily be faithfully produced.

The value of serration pitch h is preferably chosen so that the pitch d between lines 36, 38, which are either successively scanned lines of a field or adjacent lines of a frame, is equal to nit/2, where n is an odd number. The terms field and frame are used conventionally wherein the scan lines of a plurality of fields are interlaced with each other to produce a frame. In FIGURE 3, an example of the relationship is illustrated wherein the pitch d of the two lines 36 and 38 is equal to 3h/2. When such relationship exists, a relatively large 11 is permissible, since the average hue reproduced by pairs of scanning lines will be nearly equal to that obtainable from a screen having a very small h value. The limited acuity of the observers eye tends to blend the hues of the two scanning lines. Violation of the nh e relationship when h is large can result in variations in hue as a function of scanning line position, producing coarse moir patterns and/ or fluttering of hue due to the small variations in raster position normally encountered in a commercial television receiver.

In preferred forms of the serrated strip mosaic 24, successive primary color strips of the same kind have the direction of their serrations reversed. This feature is illustrated in FIGURE 3. As the electron beam scans from right to left along the scan line 36 and onto the first B strip, a serration 40 projecting to the right is encountered. As the beam scans onto the next B strip a serration 42 projecting to the left is encountered. Such reversal of serrations is provided over the entire screen for each of the three arrays of color phosphor strips R, B, and G. Such an arrangement permits the use of a relatively large 11 dimension because the average hue produced by two adjacent color groups will be nearly 4 equal to that produced by a screen with very small h. The limit acuity of the observers eye tends to blend the hues produced by adjacent color groups.

In order to facilitate fabrication of the serrated strip mosaic 24, the individual serrations may be provided with rounded rather than pointed ends. For example, a serrated edge resembling a sine wave pattern may be provided. 1

FIGURES 4 and 5 illustrate color strip mosaics 44 and 46 respectively which are modifications of the mosaic 24. The mosaics 44 and 46, like the mosaic 24, have primary color strips of widths P. The mosaics 44 and 46 differ from the mosaic 24 in the make-up of the separating secondary color strips 48 and 50, respectively, of width S. Nevertheless, the secondary color strips 48 and 50 are similar to those of the mosaic 24 in the sense that they each are constituted of sub-elemental areas of the same kind of phosphor as the two primary color strips by which they are flanked.

In FIGURE 4 each secondary color strip 48 comprises a pair of sub-elemental phosphor strips 52 and 54, each of which is of the same kind of phosphor as different ones of the flanking primary color strips and which are parallel thereto. Each of the two sub-elemental phosphor strips 52 and 54 lies contiguous with that one of the two flanking color strips which is of a different color emitting phosphor. For example, the sub-elemental strip 52, which is of green-emitting phosphor, lies next to the red-emitting primary phosphor strip R; and the subelemental strip 54, which is of red-emitting phosphor, lies next to the green-emitting primary phosphor strip G.

One advantage of the mosaic 44 compared with the mosaic 24 is that it is easier to fabricate because of the less intricate pattern design of the secondary color strip 48 thereof.

In FIGURE 5 each secondary color strip 50 comprises a multiplicity of sub-elemental phosphor dots 56. Substantially half of the sub-elemental dots of any one secondary color strip 50 are of the same kind of phosphor as one of the two flanking primary color strips, and the other half of the dots are of the same kind of phosphor as the other flanking primary color strip. FIGURE 6 is an enlargement of a portion of FIGURE 5 illustrating the dot composition of a secondary color strip 50 between a blue and a red pair of primary color strips. The dots 56 may be grouped in any one of several suitable ways. Grouping patterns which will produce a high degree of uniform intermingling of the two different kinds of phosphor dots are preferred. For example, in the mosaic 46, the dots 56 are arranged in a triangularly nested relationship in three vertical rows. Each rows comprises dots of alternately different phosphors.

In each of the three mosaics 24, 44, and 46, three different kinds of phosphors only are used to produce a mosaic color screen having characteristics simulating a mosaic of six different primary color phosphors. Yet fabrication of the mosaics 24, 44, and 46 are much less complicated than fabrication of a six color primary screen. In fabricating mosaic type phosphor screens, the usual procedure employed by the industry is to lay down a pattern of phosphor areas of one kind of phosphor using photodeposition techniques and then to repeat the process to lay down arrays of each of the other desired kinds of phosphor. In fabricating the mosaics 24, 44, and 46 the secondary color strips 32, 48, and 50 are provided with no additional photodeposition steps over that required in laying down the primary color phosphor strips. The sub-elemental areasof the secondary color strips 32, 48, and 50 are put down at the same time the array of primary color strips of the same color are deposited.

In the mosaics 24, ;44, and 46, the Widths of the primary color phosphor strips are illustrated as being equal to each other. The same is true for the secondary color strips 32, 48, and 50 of these mosaics. However, such illustration is by way of example only. In actual practice it may be desired to make the width of the red strips, blue strips, and green strips each different from the other.

Also by way of example, in the mosaics 24, 44, and 46, finite width boundaries (secondary color strips 32, 48, and 50) are provided between each pair of adjacent primary color strips. However, this feature need not be provided between all of the primary color phosphor strips. For example, secondary color strips as illustrated by the strips 32, 48, or 50 may be provided between only the red and green, the red and blue, or the green and blue primary strips.

Each of the mosaics 24, 44, and 46 are shown to be constituted of three different primary color phosphors. However, the invention may be embodied in mosaic screens having less or more than three primary color phosphors. For example, the screen may comprise a mosaic of red, green, blue, and yellow primary color phosphor strips.

The invention has been described as embodied in mosaics 24, 44, and 46 which include color phosphor strips perpendicular to the scanning lines of a raster. However, the invention may also be embodied in mosaics having color phosphor strips parallel to the scanning lines. In scanning the latter type mosaic an auxiliary deflection is generally provided which produces an undulatory scan line. Whereas the central axis of a scan line tracks a given color phosphor strip, the undulations of the scan line result in excursions onto the adjacent color phosphor strips to produce the desired secondary color rendition. Reproduction of secondary colors are improved in such a system by the presence of serrated color phosphor strips or some other color phosphor strip structure as described above which provides a finite width boundary between the primary color phosphor strips. In a serrated strip mosaic, the pitch [2 of the serrations may be chosen such that where d is the pitch of successive undulations of the scan line.

What is claimed is:

1. A color cathode ray tube comprising a screen electrode and an electron gun for projecting an electron beam onto said screen electrode, said screen electrode including a mosaic comprising:

(a) a first array of elemental areas having a first response characteristic to electron bombardment, and

(b) a second array of elemental areas having a second response characteristic to electron bombardment which is diiferent from that of said first array, and

(c) a third array of elemental areas each of which is disposed between adjacent elemental areas of said first and second arrays and which includes a plurality of discrete sub-elemental areas having at least one dimension that is substantially smaller than the smallest dimension of the elemental areas of said first and second arrays, some of said sub-elemental areas of each elemental area having said first response characteristic to electron bombardment and other of said sub-elemental areas of each elemental area having said second response characteristic to electron bombardment.

2. A color cathode ray tube including a screen electrode and an electron gun for projecting an electron beam onto said screen electrode, said screen electrode comprising:

(a) a first array of spaced-apart strip areas of one kind of phosphor particles,

(b) a second array of spaced-apart strip areas of a different kind of phosphor particles,

(c) the strip areas of said first array being interleaved with and spaced-apart from the adjacent ones of the strip areas of said second array,

(d) a third array of strip areas each of which is disposed between adjacent strip areas of said first and second interleaved arrays and which includes a plu rality of discrete sub-elemental areas of each strip area, some of said sub-elemental areas being of said one kind of phosphor and other of said sub-elemental areas of each strip area being of said different kind of phosphor, the sub-elemental areas of each strip area being orderly arranged and of discrete sizes substantially smaller than the strip areas of said first.

and second array but larger than an individual phosphor particle, and

(e) index signal generating means overlying said strip arrays.

3. A color cathode ray tube including a screen electrode and an electron gun for projecting onto said screen electrode an electron beam which is adapted to be scanned across said screen electrode in a given direction, said screen electrode comprising:

(a) a first array of spaced-apart strip areas having a given response characteristic to electron bombardment, and

(b) a second array of spaced-apart strip areas interleaved with said first array of strip areas and having a response characteristic to electron bombardment which is different from that of said first array of strip areas,

(c) said strip areas of said arrays being disposed parallel to each other and having serrated longitudinal edges.

4. A color cathode ray tube including a screen electrode and an electron gun for projecting an electron beam onto said screen electrode, said screen electrode comprising:

(a) a phosphor mosaic including a first array of strips of one kind of phosphor and a second array of strips of another kind of phosphor, said phosphor strips being disposed parallel to each other and perpendicular to the direction of intended beam scan, and

(b) index signal generating means overlying said mosaic,

(c) the strips of at least one of said arrays having serrated longitudinal edges.

5. A color cathode ray tube including a screen electrode and an electron gun for projecting onto said screen electrode an electron beam which is adapted to be scanned across said screen electrode in a given direction, said screen electrode comprising:

(a) a phosphor mosaic includinga first array of strips of one kind of phosphor and a second array of strips of another kind of phosphor, said phosphor strips being disposed parallel to each other and perpendicular to said given direction of beam scan, and

(b) an array of spaced-apart indexing strips of electron sensitive material overlying said mosaic and disposed parallel to said phosphor strips,

(0) the strips of said phosphor strip arrays having serrated longitudinal edges which are intermeshed with the adjacent ones of each other.

6. A color cathode ray tube including a screen electrode and an electron gun for projecting an electron beam onto said screen electrode, said screen electrode comprising:

(a) a first array of spaced-apart strip areas of a first kind of phosphor,

(b) a second array of spaced-apart strip areas of a second kind of phosphor,

(c) a third array of spaced-apart strip areas of a third kind of phosphor,

(d) said arrays being disposed in a common layer and being interleaved with each other,

(e) said strips having serrated edges and being disposed with their serrations meshed with the serrations of adjacent strips, and

(f) strip-like index signal generating means disposed in overlying relationship with said common layer of strip arrays.

7. A color cathode ray tube including a screen electrode and an electron gun for projecting an electron beam onto scanned across said screen electrode in a given direction,

said screen electrode comprising:

(a) a mosaic layer including a plurality of phosphor strip groups each of said groups including a redemitting phosphor strip, a blue-emitting phosphor strip, and a green-emitting phosphor strip,

(b) said phosphor strips being parallel to each other and substantially perpendicular to said given direction of beam scan,

(c) a corresponding two of the phosphor strips of each group being adjacent to each other and having their adjacent edges serrated and intermeshed With each other,

(d) a light reflective metallic layer superimposed on said mosaic layer, and

(e) index signal generating means disposed on said light reflective layer and including an array of spacedapart strip deposits arranged parallel to said phosphor strips in a systematic relationship therewith.

8. A color'cathode ray tube comprising a screen electrode and an electron gun for projecting an electron beam onto said screen electrode, said screen electrode including a mosaic comprising:

(a) a first array of spaced elemental phosphor areas, each pair of adjacent areas of which emit light of different primary colors in response to electron bombardment; and 1 (b) a second array of spaced elemental areas, each disposed between and continguous to two adjacent areas of said first array, each of said elemental areas of said second array comprising a mixture of the phosphors of the two adjacent elemental areas, whereby each emits light of a secondary color which is a 8 combination of the two primary colors emitted by the two adjacent areas of said first array, in response to electron bombardment.

9. A color cathode ray tube as in claim 8, wherein said elemental areas of said first array are spaced parallel elongated phosphor strips, and each elemental area of said second array is made up of intermeshed serrations on the sides of the two adjacentstrips of said first array.

10. A color cathode ray tube as in claim 8, wherein said elemental areas of said first array are spaced parallel elongated phosphor strips, and each elemental area of said second array comprises a plurality of sub-elemental strips of the two phosphors of the adjacent elemental areas.

11. A 'color cathode ray tube as in claim 8, wherein said elemental areas of said first array are spaced parallel elongated. phosphor strips, and each elemental area of said second array is made up of a multiplicity of subelemental dots of the two phosphors adjacent elemental areas.

References Cited by the Examiner UNITED STATES PATENTS 2,683,833 7/ 1954 Zaphiropoulos. 2,702,873 2/ 1955 Lawrence 31392 2,711,493 6/1955 Lawrence 313-92 2,745,035 5/ 1956 Lawrence. 2,764,628 9/ 1956 Bambara. 2,790,920 4/1957 Todd.

JOHN W. HUCKERT, Primary Examiner.

DAVID J. GALVIN, Examiner. 

1. A COLOR CATHODE RAY TUBE COMPRISING A SCREEN ELECTRODE AND AN ELECTRON GUN FOR PROJECTING AN ELECTRON BEAM ONTO SAID SCREEN ELECTRODE, SAID SCREEN ELECTRODE INCLUDING A MOSAIC COMPRISING: (A) A FIRST ARRAY OF ELEMENTAL AREAS HAVING A FIRST RESPONSE CHARACTERISTIC TO ELECTRON BOMBARDMENT, AND (B) A SECOND ARRAY OF ELEMENTAL AREAS HAVING A SECOND RESPONSE CHARACTERISTIC TO ELECTRON BOMBARDMENT WHICH IS DIFFERENT FROM THAT OF SAID FIRST ARRAY, AND (C) A THIRD ARRARY OF ELEMENTAL AREAS EACH OF WHICH IS DISPOSED BETWEEN ADJACENT ELEMENTAL AREAS OF SAID FIRST AND SECOND ARRAYS AND WHICH INCLUDES A PLURALITY OF DISCRETE SUB-ELEMENTAL AREAS HAVING AT LEAST ONE 